JPH02303519A - Exhaust gas dry desulfurization method - Google Patents

Abstract

PURPOSE:To attain a high desulfurization rate by previously adding a bromine compd. into fuel at the time of blowing calcium carbonate into exhaust gases of various combustion furnaces, etc, and removing sulfur oxides. CONSTITUTION:The calcium carbonate is blown into the exhaust gases of the various combustion furnaces 6, such as boilers and heating furnaces, and a waste incineration furnace 6, to remove the sulfur oxide. The bromine compd. (e.g. methane bromide) is previously added into the fuel. As a result, the high desulfurization rate which is not heretofore attained in the conventional lime- blowing method is attained. The smaller ratio of the So2 in the exhaust gases and the calcium carbonate of the desulfurizer (Ca/S) is necessitated and, therefore, the desulfurizer is effectively utilized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the treatment of sulfur oxides (S
Ox) can be effectively removed using a dry method, thereby contributing to the improvement of atmospheric environmental pollution.

[Prior art and its problems] Conventionally, as a method for removing SOx from combustion exhaust gas of this type, a wet lime-gypsum method has been known as a completed technology. This method has already been established as an advanced technology and is a process with many proven results.

However, since this is a wet method, there are problems such as diffusion of exhaust gas after desulfurization treatment and generation of white smoke. Incidentally, the diffusion of the exhaust gas and the generation of white smoke are dealt with by reheating the exhaust gas, and although this has been technically solved, it is an economical burden. Furthermore, since this method requires a large amount of water, its application is limited in regions with limited water resources. Therefore, there are high expectations for the development of a dry desulfurization method to replace the wet method.

The main processes being researched as dry desulfurization methods include electron beam irradiation method, activated carbon method, and lime (calcium carbonate) method.
There are blowing methods, and lime slurry spraying methods, which can also be called semi-dry methods.

Here, the electron beam irradiation method and the activated carbon method are complex in terms of equipment, and although a relatively large pilot plant or demonstration plant has been constructed and operated, it will still take time to put them into practical use.

The lime blowing method involves blowing fine powder of calcium carbonate into the combustion furnace or into the flue outside the furnace to remove SO in the exhaust gas.
This is a method of absorbing and removing x. Calcium sulfate produced by absorbing SOx is removed by a precipitator after cooling the exhaust gas.

In other words, it is the simplest method in terms of process and is also economically superior. However, the problem is that the reaction rate is low due to the gas/solid phase reaction, and the desulfurization rate is low. In order to increase the desulfurization rate, it is possible to increase the reaction rate and effectively utilize the desulfurization agent by injecting a large excess of this desulfurization agent (still the desulfurization rate is not sufficient) or by making the desulfurization agent into ultrafine particles and increasing its surface area. Efforts are being made to increase the rate.

However, its desulfurization rate is still low, and it has not reached the point where it can be put to practical use.

The lime slurry spraying method was devised as one of the means to improve this low reaction rate.

In this method, since the lime slurry is sprayed as fine particles, the reaction rate increases, and at the same time, the moisture in the slurry is evaporated by the sensible heat of the exhaust gas, and the recovery is performed as fine powder of calcium sulfate. Although this method has been put into practical use mainly in West Germany and the United States, it still has basic problems such as the desulfurization rate not being as high as the wet method and the need for water for slurry preparation.

The outline of the research and development of the dry method has been described above, but the ideal dry desulfurization method would be the lime blowing method, which has an improved desulfurization rate.

[Means for Solving Problems] The present invention has been made in view of the above-mentioned circumstances, and relates to an improvement of the lime blowing method. As mentioned above, the lime blowing method is a simple and inexpensive method, but it has the drawback of low reaction rate. The method according to the invention solves this problem very simply and effectively.

That is, the method is characterized in that a bromine compound is added in advance to the fuel before carrying out the lime blowing desulfurization method.

Here, the bromine compound is a compound containing bromine, such as ammonium bromide and methane bromide (a compound in which hydrogen in methane is replaced by one or more bromine).

The method according to the present invention is not particularly technically difficult; for example, when the fuel is coal, it can be achieved by mixing the coal with fine powder of the above-mentioned bromine compound or impregnating it as an aqueous solution.

If the fuel is liquid, a bromine compound may be dissolved and added to it, and if it is gas, its fine powder may be mixed into the fuel. In other words, by simply applying the conventional lime blowing method currently under research and development to the exhaust gas produced by burning fuel to which bromine has been added in advance, a significant improvement in the desulfurization rate can be observed.

Although the mechanism of action of this type of bromine compound has not been fully elucidated, it is thought to be as follows. The rate-determining step in the desulfurization reaction in the lime blowing method is said to be the oxidation and absorption reaction of SO2 on the lime surface, and especially the diffusion of SOx in the shell (film) of calcium sulfate formed on the surface.

In other words, once a shell of calcium sulfate is formed, SOx
cannot reach the center and the reaction stops. Therefore, the SOx removal rate is low and the lime utilization rate is also low. This issue could be solved to some extent by making the lime particles smaller, but there are limits. Even if S02 was previously oxidized to SO3 in this reaction, it does not seem possible to solve this problem of diffusion within the solid. In other words, it is difficult to believe that the bromine compound acts as a catalyst for the oxidation of S02. In reality, the SO2 concentration at the outlet of the combustion furnace is the same when bromine compounds are present in the fuel and when bromine compounds are not present;
No evidence of accelerated oxidation of 2 was obtained. (This confirmation was conducted in a coal-fired furnace, and S
Since it is not easy to analyze 03, we compared the measured values with the S02 infrared analyzer. If the oxidation to S03 is large, the infrared analyzer will not measure SO3, so the S02 concentration will be measured low.

) Therefore, it is considered that the effect of the bromine compound in the present invention contributes to a change in the physical state of the desulfurizing agent, ie, calcium carbonate, or the formed calcium sulfate layer.

For example, calcium bromide has a decomposition temperature of 730.degree. C. and a melting point of 810.degree. C., making it difficult to form a shell, making it likely that adsorption and diffusion of S02 will occur.

[Effects of the Invention] According to the improved lime blowing method of the present invention, a high desulfurization rate that could not be achieved with the conventional lime blowing method can be obtained.

Furthermore, the ratio of S02 in the exhaust gas to calcium carbonate of the desulfurizing agent, Ca/S, can be small, so the desulfurizing agent can be used effectively.

In other words, this method is almost the same in terms of equipment as the lime blowing method, which is the simplest method among conventional dry desulfurization methods, and is a simple method of adding bromine compounds to the fuel. A desulfurization rate comparable to that of the above can be achieved, and it can economically advantageously contribute to the improvement of air pollution.

[Example] The present invention will be specifically described with reference to Examples and Comparative Examples.

Comparative Example 1 In this comparative example, an example of the measurement results of the desulfurization rate in the lime blowing method, which is a conventional technique, is shown in order to clarify the features of the example described below.

The attached drawing is a flow sheet showing an outline of the apparatus for carrying out the tests in this comparative example and the following examples. This device mainly consists of a pulverized coal-fired combustion chamber (6) and a reaction chamber (1) on the downstream side thereof. The combustion rate is 10 kg/hour, and it is possible to control the combustion temperature by burning auxiliary propane and adjust the S02 concentration in the exhaust gas by injecting S02 gas. The combustion chamber (6) has an inner diameter of 350 mm and a height of 450 av. The reaction chamber (1) for desulfurization consists of a stainless steel tube with an inner diameter of 330n+m and a height of 4m. The reaction chamber (1) can be controlled to a predetermined temperature by an electric heater (2) provided on its outer surface. Fine powder of calcium carbonate, which is a desulfurizing agent, is blown into the reaction chamber (1) on an air stream. The concentrations of O2 and S02 in the exhaust gas are measured using analyzers (7) (8) installed at the outlet of the reaction chamber (1) and the outlet of the bag filter (3).
) are measured respectively. Exhaust gas is air heater (4)
It is cooled by a gas cooler (5) and a bag filter.
(3) Dust is removed and released into the atmosphere. In the same figure, (9)
indicates a thermometer, and (10) indicates a flowmeter.

Using the apparatus configured as described above, finely ground calcium carbonate was blown as a desulfurization agent into the exhaust gas generated by coal combustion. Table 1 shows the desulfurization rate for this test. Here, the reaction temperature is 1300℃, 1 degree of 5O2i is about 900p
Adjusted to pm. The oxygen concentration was 6.1%. Moreover, the reaction time was 3 seconds.

Table 1 Example 1 In the lime blowing method described in Comparative Example 1, a desulfurization test was conducted using fuel in which finely ground methane bromide was mixed into coal. Pulverized coal containing 3.4% methane bromide and pulverized coal containing 0.34% methane bromide were prepared as fuel, and these were sequentially combusted.

The operating conditions of the apparatus in this example are as follows.

Fuel supply rate + 8.92Kg/hour Air ratio: 1.41 Exhaust gas amount: 94, ONm3/hour Desulfurization agent supply rate (CaCO3): 0.66kg/hour Reaction time = 3.3 seconds Reaction temperature: 1340℃ 8024℃: 830 ppm 02 concentration: 6.1% Ca/S molar ratio: 1.89 As a result of the test, when coal containing 3.4% bromide methane was used, a desulfurization rate of 99.0% was obtained, and 0.34 %, a desulfurization rate of 93.2% was obtained. This result corresponds to the desulfurization rate of 5 in the equivalent test of Comparative Example 1 mentioned above.
Compared to 4%, the desulfurization rate is significantly improved.

Example 2 In the lime blowing method described in Comparative Example 1, a desulfurization test was conducted using fuel in which finely ground ammonium bromide was mixed into coal. Ammonium bromide as fuel4.
Pulverized coal containing 2% ammonium bromide and pulverized coal containing 0.42% ammonium bromide were prepared, and these were sequentially combusted.

The operating conditions of the apparatus in this example are as follows.

Fuel supply speed +8.12kg/hour Air ratio: 1.41 Exhaust gas amount: 85. 3Ntx ”/hour Desulfurization agent supply rate (CaCO3) 70.57kg 1 hour Reaction time 23.7 seconds Reaction temperature: 1260℃ 5O2fL degree: 830ppm O2 concentration: 6.1% Ca / S molar ratio 41.81 Test results, When using coal containing 4.2% ammonium bromide, a desulfurization rate of 98.8% was obtained, and a desulfurization rate of 0.42% was obtained.
%, a desulfurization rate of 94.2% was obtained. This result shows a desulfurization rate higher than any result under other conditions, not to mention the desulfurization rate of 54% in the equivalent test of Comparative Example 1 described above.

Implementation fq3 Under exactly the same conditions as in Example 2 (coal combustion containing 0.42% ammonium bromide), the desulfurization agent supply rate (CaCO3) was set to 0.
reduced to 44 kg/hour (Ca/S molar ratio: 1.40),
The desulfurization rate was measured.

As a result, a desulfurization rate of 90.3% was obtained.

[Brief explanation of drawings]

The drawing is a flow sheet showing the test method. that's all

Claims (1)

[Claims] An exhaust gas dry desulfurization method characterized by adding a bromine compound to the fuel in advance, in a method of removing sulfur oxides by injecting calcium carbonate into the exhaust gas of boilers, various combustion furnaces such as heating furnaces, and garbage incineration furnaces. .